The present invention generally relates to the sealing of nozzles on fluid ejection devices, and more particularly, to thermoplastic polymer films sealing the nozzles of fluid ejection devices.
Over the past decade, substantial developments have been made in the micro-manipulation of fluids in fields such as electronic printing technology using inkjet printers. The ability to maintain a viable releasable seal of both input and output nozzles or channels in such products is very desirable.
One of the major problems of maintaining a robust seal to micro fluidic channels is the ability, during shipping, handling, and storage, to prevent fluid from leaking out of the channel as well as preventing external material from clogging or entering the channel. The desirable attributes of a seal for micro fluidic channels include the prevention of evaporation, contamination, and intermixing of fluids between channels. In addition, the ability to remove the seal while minimizing the amount of residue left on the input and/or output nozzles or channels is also desirable. Further, it is also desirable that the seal is materially compatible with the fluid (i.e. the seal is not degraded over time by the fluid).
An inkjet print cartridge provides a good example of the problems facing the practitioner in sealing micro fluidic channels. There is a wide variety of highly-efficient inkjet printing systems currently in use, which are capable of dispensing ink in a rapid and accurate manner. Conventionally, the loss of ink and or clogging of the ink ejection nozzles is prevented by either using a capping device or by using a pressure sensitive tape (PSA) (see for example U.S. Pat. No. 5,414,454) in most of these systems. However, there is a corresponding need for improved sealing technologies, as inkjet-printing systems continue to provide ever-increasing improvements in speed and image quality.
Fluid ejection cartridges typically include a fluid reservoir that is fluidically coupled to a substrate that is attached to the back of a nozzle layer containing one or more nozzles through which fluid is ejected. The substrate normally contains an energy-generating element that generates the force necessary for ejecting the fluid held in the reservoir. Two widely used energy generating elements are thermal resistors and piezoelectric elements. The former rapidly heats a component in the fluid above its boiling point causing ejection of a drop of the fluid. The latter utilizes a voltage pulse to generate a compressive force on the fluid resulting in ejection of a drop of the fluid.
In particular, improvements in image quality have led to both a decrease in the size of the nozzles as well as the complexity of ink formulations that increases the sensitivity of the cartridge to residue. Smaller nozzles are more susceptible to plugging from any residue left in a nozzle region when the seal is removed. Nozzles are also more susceptible to clogging from residue left on the nozzle layer that is swept into a nozzle by a service station wiper when the nozzle layer is cleaned. In addition, improvements in image quality have led to an increase in the organic content of inkjet inks that results in a more corrosive environment experienced by the material sealing the nozzles. Thus, degradation of the sealing material by more corrosive inks raises material compatibility issues. In addition, improvement in print speed has typically been gained by utilizing a larger printhead resulting in an increased print swath. The larger printhead results in a larger number of nozzles to be sealed and thus the need to maintain a leak tight seal over a greater area.
Conventional capping devices typically seal the inkjet nozzles using a mechanical structure to apply pressure to a compliant material (typically an elastomeric or resilient foam material), that is pressed or forced against the nozzles resulting in a seal. These devices, however, can suffer leakage during shipping, handling, and storage due to vibration, rough handling, temperature and humidity fluctuations etc., which can result in clogged nozzles or spillage of ink in the cartridge container. This problem is exacerbated when it occurs in ink cartridges containing multiple inks, resulting in ink mixing that typically produces poor color rendition when printed. Although conventional capping materials can be more compatible with the newer aggressive or corrosive inks, the increased print swath increases the likelihood of leaks due to thermal expansion and the bending properties of both the printhead and the capping device.
Conventional PSA tapes on the other hand typically seal the inkjet nozzles using a pressure sensitive adhesive. The PSA tape is generally constructed of a base film with an acrylate based pressure sensitive adhesive layer used to seal the nozzles as shown schematically in FIG. 1. The base film is normally made of polyethylene terephthalate commonly referred to as polyester (PET) or polyvinyl Chloride (PVC). The use of thin PSA tapes has resulted in improving the resistance to environmental variation due to dimensional changes caused by temperature and humidity excursions. PSA tapes have also provided some improvement in durability in regards to vibration, thus, improving upon some of the problems associated with capping devices. However, a PSA tape applied over an irregular surface, such as a protrusion, a stepped structure or a discontinuous surface, can result in the gradual peeling or lifting of the PSA tape resulting in leakage, especially over longer periods of time. The gradual lifting can also result in the formation of an air pocket between the tape and the nozzle plate, allowing ink to flow into this region which will then react or corrode materials such as the encapsulant that protects the electrical traces. Ultimately this may lead to electrical shorts and the print cartridge may fail.
As noted above and shown in a simplified isometric view in FIG. 1 most PSA tapes generally consist of a base film 11 and an adhesive layer 21 with a liner 31 and/or release layer 41 (typically polydimethylsiloxane {PDMS}). During application the liner 31 is removed and discarded. The adhesive layer 21 is bonded to the nozzle layer, using pressure, forming a seal. The adhesive layer is typically an elastomer mixture with large quantities of small molecular additives having a low molecular weight. The additives typically include plasticizers, tackifiers, polymerization catalysts, and curing agents. These low molecular weight additives are added primarily to change the glass transition temperature (Tg) of the material and to provide tack.
Since these additives are low in molecular weight compared to the polymer molecular weight they can both be leached out of the adhesive layer by the ink, react with ink components, or both, more easily than the polymer backbone. In either case, whether the low molecular weight material reacts with, or is leached out by the ink, the adhesive layer of the PSA tape is left with a weakened cohesive strength which can result in a residue being left behind when the tape is removed. In addition, the reaction between these low molecular weight additives and ink components can also lead to the formation of precipitates or gelatinous materials, which can further result in clogging of the nozzles.
The interaction of these low molecular weight additives and the ink components can also give rise to a weakening of the base/adhesive film interface. Thus, if the strength of this interface is sufficiently degraded, the adhesive layer of the tape can remain on the print cartridge when the user attempts to pull the tape off before inserting the cartridge into the printer. The material compatibility of both the base film as well as the adhesive film is carefully chosen for each ink. The material compatibility of the ink/additive interactions as well as the general ink/polymer interactions should be considered.
Regardless of the method used to eject the fluid, once a fluid ejection cartridge is manufactured, filled with fluid, and tested there is a need to seal the nozzle or nozzles to prevent leakage, reduce evaporation of the fluid, and to hinder contamination of the fluid. Thus, practitioners are often faced with difficult choices between capping devices (greater ink robustness); PSA tapes (better sealing properties) and changes in ink formulation to meet the shipping, handling, and storage requirements for a particular fluid ejection cartridge.
Thus a sealing system that prevents fluid leakage, evaporation, contamination, and intermixing between channels, as well as being easily removable while minimizing the residue left on a variety of nozzle plates and is compatible with a variety of inks would be an advance in the art.
A fluid ejection cartridge includes an ejector head having at least one nozzle and a fluid reservoir containing an ejectable fluid, fluidically coupled with the at least one nozzle. The fluid ejection cartridge has a tape that includes a thermoplastic polymer film in contact with and releasably bonded to the nozzles.